Mixing devices in the field of preparing instant beverages are known. An example which may be mentioned is WO 03/068039.
Such mixing devices are required in order to mix the liquid, usually hot or cold water, with the instant ingredient, in the case of WO 03/068039 an instant powder. Referring to said example WO 03/068039, such a mixing device has a mixing chamber containing a rotor. The mixing chamber is usually subdivided into an inlet chamber and a rotor chamber. At the top, the inlet chamber is provided with an access opening through which portions of instant powder are delivered to the inlet chamber. The inlet chamber furthermore has an inlet mouth by means of which the hot water is supplied. When the inlet chamber is round and the inlet is oriented radially, mixing occurs in the inlet chamber as a result of the liquid making a circular motion. From the inlet chamber, the liquid with the instant powder passes to the rotor chamber in which the rotor is located. The rotor is, as is also the case in WO 03/068039, usually arranged so that it rotates about a horizontal axis of rotation. As a result thereof, a pipe bend is usually provided between the inlet chamber and the rotor chamber. The rotor may perform various functions, optionally in combination, and may, partly for this reason, have various forms. One function is to improve the mixing. Another function is foaming up the beverage by mixing in air or by another way. Yet another function is a conveying function. Furthermore, an outlet is connected to the mixing chamber, usually to the rotor chamber near the rotor, in order to discharge the mixture produced, generally into a container, such as a beaker, mug, cup or pot, from which the beverage can be drunk or poured. The outlet is generally horizontally oriented and has a discharge part at the end having an outflow opening which is directed downwards by means of a bend.
The known mixing devices for preparing an instant beverage have various shortcomings, that is to say there are various points which can be improved upon.
One of the points which can be improved upon is the operation of the rotor. There are many known patent applications which are aimed at improving the operation of the rotor.
Thus, it is known from WO 03068039 to design the surface of revolution defined by the rotating rotor as a tapering surface and to make it of such a length and size that it results in a high foaming efficiency. The surface of revolution of the rotor is in this case provided with grooves which extend along a curved line in the axial direction. The solution in this case consists of specific angles for the taper of the surface of revolution, specific rotation speeds, specific gap widths between the surface of revolution of the rotor and the surrounding peripheral wall zone of the rotor housing; specific gap widths between the axial end surfaces of the rotor and the rotor housing.
Furthermore, reference may be made to EP 1.639.924, which, taking the publication mentioned above as starting point, discloses further features of the surface of revolution of the rotor in order to improve the operation of the rotor.
In order to prevent problems with the operation of the rotor as a result of lumps of instant powder which have not dissolved, EP 1.116464 describes providing a screen upstream of the rotor which stops such lumps of instant powder which have not dissolved.
All in all, various shapes of rotors are known, the design of which is usually based on the starting point of enlarging the contact surface of the rotor, which is then often effected by means of recesses and/or ribs in the surface of revolution of the rotor.
It is an object of the present invention to further improve the effect of the rotor for the purpose of foam-formation and/or improved mixing action and/or otherwise.